Adhesives have been used for a variety of marking, holding, protecting, sealing and masking purposes. Adhesive tapes generally comprise a backing, or substrate, and an adhesive. One type of adhesive, a pressure sensitive adhesive (PSA) is particularly preferred for many applications.
PSAs are well known to one of ordinary skill in the art to possess certain properties at room temperature including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength. The most commonly used polymers for preparation of PSAs are natural rubber, synthetic rubbers (e.g., styrene/butadiene copolymers (SBR) and styrene/isoprene/styrene (SIS) block copolymers), and various (meth)acrylate (e.g., acrylate and methacrylate) copolymers. With the exception of several (meth)acrylates, which are inherently tacky, these polymers are typically blended with appropriate tackifying resins to render them pressure sensitive.
A variety of adhesive articles have been described that are heat-responsive. By this it is meant that upon the application of heat to an adhesive article a response is generated. In some articles the response is to form a bond, in other instances it is to break a bond. In general four types of such articles have been described. The first group are ones in which the application of heat to an adhesive article is applied to form a bond. The second group of references is so called processing tapes, where a tape is applied to a substrate for one or more processing steps and then removed. The third group includes references to adhesive articles where an additive is present in the adhesive that is thermally responsive. The fourth group includes articles that contain heat responsive materials, either polymeric materials or metallic materials.
An example of the first group is EP Patent Publication No. 1,130,070 which describes thermally shrinkable films or labels for containers where the labels or films are affixed by the process of a) coating the thermally shrinkable film or label with a radiation curable adhesive, b) applying the film or label to the container, c) radiation curing the adhesive, and d) heating the container to shrink the film or label to permanently affix it to the container.
Examples of the second group, processing tapes, include a series of US Patent Publication Nos. 2008/0131634, 2010/0252185, and 2010/0279491 (all to Kiuchi et al.). These references describe adhesive coated sheets and tapes that are self-rolling. The sheets or tapes include a shrinkable film layer which upon shrinking rolls upon itself causing a peeling release from substrates to which the sheet or tape are adhered. U.S. Pat. No. 7,063,765 (Kudo et al.) describes a processing tape for wafer dicing in which adhesive layers are present in which the adhesion of the adhesive layers can be reduced by a chemical reaction. A method of processing a wafer article that includes a sheet containing sequentially, a first substrate, a first adhesive layer, a second substrate, and a second adhesive layer is described where the sheet is affixed to a wafer, the wafer is diced, the first substrate and first adhesive layer are removed by reducing the adhesion of the first adhesive layer, the wafer is divided into a plurality of chips and the second substrate and second adhesive layer are removed by reducing the adhesion of the second adhesive layer. PCT Publication No. WO 98/55280 describes a veneer tape that can be used to maintain a plurality of wood veneer substrates in fixed relation to each before and during a lamination process and is cleanly removable from the substrates following the lamination process. The tape backing may include a heat-shrinkable film.
Examples of the third group of adhesive articles where the adhesives contain heat responsive additives include US Patent Publication No. 2009/0053478 (Sakashita) which describes a functional film formed on a film formation substrate. The method of making the functional film includes: a) forming an electromagnetic wave absorbing layer on the substrate; b) forming a separation layer on the electromagnetic wave absorbing layer by using an inorganic material that forms a gas upon heating; c) forming a layer to be peeled containing a functional film; and d) applying electromagnetic wave to electromagnetic wave absorbing layer to reduce the bonding strength between the layer to be peeled and the substrate. Another example is PCT Publication No. WO 00/40648 which describes a heat debondable adhesive composition. The heat debondable adhesive compositions comprises a curable resin and a heat expandable inorganic material.
Examples of the fourth group of adhesive articles include materials that are heat responsive. US Patent Publication No. 2011/0281045 (Goubard, et al.) describes multilayer articles such as labels that include a hot melt pressure sensitive adhesive layer, a printable support layer, which may comprise a heat-shrinkable material, and a protective layer. The labels are removable by immersing in hot basic aqueous solutions. U.S. Pat. No. 5,441,810 (Aizawa et al.) describes an adhesive sheet comprising a substrate with a rubber-like elastic layer, a heat-expandable layer, and an adhesive layer. Some of the heat responsive articles include materials that are described as shape memory polymers. Shape memory polymers are materials that are formed in one shape, deformed to a second shape, and revert to their original shape upon the application of heat. U.S. Pat. No. 5,888,650 (Calhoun et al.) describes temperature-responsive adhesive articles with: a) a temperature-responsive carrier; and b) a thermomorphic pressure sensitive adhesive coated on at least a portion of the carrier. The articles have a wide range of bonding and de-bonding properties. U.S. Pat. No. 6,773,535 (Wetzel) describes a separable bonding system including two opposed rigid adherends and deformed shape memory alloy element disposed between and adhesively bonded to facing surfaces of the two rigid adherends. The shape memory alloy member is mechanically strained to form a deformed shape memory alloy member. The temperature is elevated sufficient to transform the deformed shape memory alloy member to a recovered shape, thereby weakening the adhesive bonds to the two rigid adherends. US Patent Publication No. 2010/0316845 (Rule et al.) describes adhesive articles that contain shape memory polymer backings and are debondable from substrates or adherends with the application of heat. U.S. Patent Application Ser. No. 61/509,250, filed Jul. 19, 2011 with the title “DEBONDABLE ADHESIVE ARTICLE AND METHODS OF MAKING AND USING THE SAME” describes debondable adhesive articles including adhesive layers on opposing sides of shape-memory polymer sheet that includes a plurality of slits therein. The article can be debonded by heating the article to a temperature equal to or greater than a transition temperature for the shape-memory polymer sheet.